1. Field of the Invention
The present invention relates to a method of manufacturing a shutter. More particularly, the present invention relates to a method of manufacturing a shutter for a disc cartridge in which a recording medium is accommodated.
2. Background of the Invention
It is customary that disk-shaped recording media, such as magnetic disks and optical discs, are accommodated in disc cartridges in order to prevent recording media from being smudged and damaged. Disc cartridges includes each a cartridge body in which a recording medium is accommodated and a shutter attached to the cartridge body. Openings are formed respectively through the front and rear surfaces of the cartridge body so that data can be recorded on and/or reproduced from the recording medium by a head assembly. These openings are opened and closed by the shutter concurrently with the loading operation or eject operation of the disc cartridge on or from a recording and/or reproducing apparatus. The shutter is formed so as to have a substantially U-letter shaped cross-section using either a metal material or synthetic resin material. The shutter is attached to the cartridge body along its one side surface so as to straddle the cartridge body and to be freely slidable therealong. When the disc cartridge is not in use, the above openings are closed by the shutter so that the recording medium can be prevented from being smudged or damaged.
Most of the shutters are, from a strength standpoint, generally made of metal, such as a stainless steel or the like. As a manufacturing method in this type of case, it has been proposed to punch out a plate-shaped metal material, and then shape the punched-out member to have substantially U-shaped cross-section using a single bending operation. The shutter thus obtained includes a pair of plate-shaped portions which open and/or close the openings of the above-mentioned cartridge body. EP-A-343844, for example, will be referred to in order to provide a better understanding of the above-mentioned shutter structure and manufacturing.
However, a drawback is encountered in that a residual stress tends to remain in the shutter which is formed using this single bending process and induce the problem that the spacing between the free ends of the pair of plate-shaped portions tends to increase with the passing of time or shock. Therefore, the spacing between the free ends of the shutter often increases with aging at normal or ambient temperatures. As a result, it is frequently observed that the two plate-shaped portions of the shutter flair out from the front and rear surfaces of a cartridge body. Even if a disc cartridge is dropped from a height of only about one meter, the spacing between the free ends of the two plate-shaped portions of the shutter tends to increase considerably. Accordingly, when a disc cartridge is ejected from a recording and/or reproducing apparatus, the shutter is sometimes caught by members disposed within the recording and/or reproducing apparatus so that the disc cartridge cannot be ejected or a similar type of trouble occurs.